1. Field of the Invention
The present invention relates to expansion joints for roadways.
2. Description of the Prior Art
It is common to fill channels or gaps between sections of roadway surfaces with some sort of joint. The gaps occur particularly in bridge decks and viaducts, and the joint seals the gap against ingress of surface water and debris. One type of expansion joint that has been known for a number of years is formed from extruded rubber which connects adjacent sections of roadway. One such joint, for use as a buried joint below the road surface, is disclosed in UK Patent Specification No. 1526194.
A second and more recent type of joint uses fluid-polymers which are poured into the channel which is to be sealed. These are cheaper and easier to install than the extruded rubber joints and also provide fewer problems when the roadway is re-surfaced. With such fluid-polymer joints, the channel between the blocks of the roadway surface is filled with a plug of packing material and the fluid-polymer is poured into the gap. The fluid-polymer then sets in situ. The joint thus produced has a plastic quality, so that if relative movement of the roadway blocks occurs the joint alters shape to fill any resultant gap.
It is also known to provide a rigid core in the fluid-polymer, to minimise impact damage to the fluid-polymer and to act as a support. For example, in U.S. Pat. No. 3,827,204 a tape of glass cloth is provided in the channel between two layers of the settable polymer. In order to prevent the joint from being dislodged from the channel, the fluid-polymer should adhere to the channel.
However the use of a fluid-polymer causes problems. If the set fluid-polymer is plastic in its behaviour then the impact of traffic on the joint has the effect of forcing the fluid-polymer out of the channel and pushing it forward in the direction of the direction of the dominant traffic flow. As the material is plastic, this results in permanent deformation of the joint. Permanent deformation can be avoided by using an elastic fluid-polymer; the fluid-polymer returning to its original shape after deformation. However, this raises a different problem, namely that the elastic deformation puts great strain on the sides of the channel to which the set fluid-polymer adheres. The fluid-polymer material must adhere to the roadway surface sufficiently to prevent it becoming dislodged but also must not load the surface too strongly, otherwise deformation of the joint causes unacceptable stresses in the edges of the roadway.
Thus if the joint is used between the edge of a bridge (normally a concrete surface) and the edge of the approach road (normally an asphalt surface) polymer materials are known which could be used which adhere to both surfaces extremely well. It has been found however that deformation of the joint causes fracture of the edges of the asphalt because the latter is not sufficiently strong to withstand the stresses exerted on it. It has not proved possible to find a fluid-polymer which does not either become permanently distorted or cause unacceptable loading of the roadway surfaces.